Technical Field
The present disclosure relates to an aluminum alloy wire rod used as a wire rod of an electric wiring structure, an aluminum alloy stranded wire, a coated wire, a wire harness, and a method of manufacturing an aluminum alloy wire rod.
Background
In the related art, a so-called wire harness has been used as an electric wiring structure for transportation vehicles such as automobiles, trains, and aircrafts, or an electric wiring structure for industrial robots. The wire harness is a member including electric wires each having a wire rod made of copper or copper alloy and fitted with terminals (connectors) made of copper or copper alloy (e.g., brass). With recent rapid advancements in performances and functions of automobiles, various electrical devices and control devices installed in vehicles tend to increase in number and electric wiring structures used for devices also tends to increase in number. On the other hand, for environmental friendliness, lightweighting of transportation vehicles is strongly desired for improving fuel efficiency of transportation vehicles such as automobiles.
As one of the measures for achieving lightweighting of transportation vehicles, there have been, for example, continuous efforts in the studies of using aluminum or aluminum alloys as a wire rod of an electric wiring structure, which is more lightweight, instead of conventionally used copper or copper alloys. Since aluminum has a specific gravity of about one-third of a specific gravity of copper and has a conductivity of about two-thirds of a conductivity of copper (in a case where pure copper is a standard for 100% IACS, pure aluminum has approximately 66% IACS), an aluminum conductor to have a cross sectional area of approximately 1.5 times greater than that of a copper conductor to allow the same electric current as the electric current flowing through the copper conductor to flow through the aluminum conductor. Even an aluminum conductor having an increased cross section as described above is used, using an aluminum conductor is advantageous from the viewpoint of lightweighting, since an aluminum conductor has a mass of about half the mass of a pure copper conductor. Note that, “% IACS” represents a conductivity when a resistivity 1.7241×10−8 Ωm of International Annealed Copper Standard is taken as 100% IACS.
However, it is known that pure aluminum wire rods, typically an aluminum alloy wire rod for transmission lines (JIS (Japanese Industrial Standard) A1060 and A1070), is generally poor in its durability to tension, resistance to impact, and bending characteristics. Therefore, for example, it cannot withstand a load abruptly applied by an operator or an industrial device while being installed to a car body, a tension at a crimp portion of a connecting portion between an electric wire and a terminal, and a cyclic stress loaded at a bending portion such as a door portion. On the other hand, an alloyed material containing various additive elements added thereto is capable of achieving an increased tensile strength, but a conductivity may decrease due to a solution phenomenon of the additive elements into aluminum, and because of excessive intermetallic compounds formed in aluminum, a wire break due to the intermetallic compounds may occur during wire drawing. Therefore, it is essential to limit or select additive elements to provide sufficient elongation characteristics to prevent a wire break, and it is further necessary to improve impact resistance and bending characteristics while ensuring a conductivity and a tensile strength equivalent to those in the related art.
For example, aluminum alloy wire rods containing Mg and Si are known as strength aluminum alloy wire rods having characteristics mentioned above. A typical example of this aluminum alloy wire rod is a 6xxx series aluminum alloy (Al—Mg—Si based alloy) wire rod. Generally, the strength of the 6xxx series aluminum alloy wire rod can be increased by applying a solution heat treatment and an aging treatment.
For example, Japanese Patent No. 5367926 discloses a conventional 6xxx series aluminum alloy wire used for an electric wiring structure of the transportation vehicle. An aluminum alloy wire disclosed in Japanese Patent No. 5367926 provides an aluminum alloy wire that is excellent in bending fatigue resistance, tensile strength and conductivity.
However, when attaching a wire harness to a vehicle, the wire harness is bent into a wavy shape at a plurality of points to conform to the layout and installation. Thus, the higher the strength, the more the force is required for bending, and it becomes a burden on workers. Also, it may be bent to nearly 180°, and a wire break may occur at such a part where a severe bending is required. Thus, there is a need for a flexible aluminum electric wire that a high strength usable for a small-sized wire and can be bent by a minimum force. However, with the conventional embodiment such as Japanese Patent No. 5367926, it was not possible to sufficiently meet such a need.
The present disclosure is related to providing an aluminum alloy wire rod used as a wire rod of an electric wiring structure that is usable for a small-sized wire due to a high strength and that has flexibility and can be bent with a reduced force, and also less likely to cause a wire break even if a severe bend such as 180° is applied, an aluminum alloy stranded wire, a coated wire, a wire harness, and a method of manufacturing an aluminum alloy wire rod.
The inventors carried out various studies, and found that an aluminum alloy wire rod having flexibility while maintaining an excellent tensile strength can be manufactured by controlling heat treatment conditions in an aluminum alloy wire rod manufacturing process to control crystal orientation, and obtained the present disclosure based on such findings.